1. Field of the Invention
The present invention relates to extractors for removing broken threaded fasteners such as broken bolts, and more particularly, to a broken fastener extractor comprising a drill head with a collet to grab the bolt, and including guide means for starting the drill in the center of the broken bolt.
2. Description of Related Art including Information Disclosed under .sctn..sctn.1.97 to 1.99
The present invention is an improvement over my prior U.S. Pat. Nos. 4,604,917 issued Aug. 12, 1986 and 4,777,850 issued Oct. 18, 1988.
When the drive head is broken off a bolt, it becomes a difficult, time-consuming process to remove the stud portion of the bolt which remains in the threaded bore beneath the support surface where the bolt had originally been inserted. Conventionally, removal of the stud requires that a hole be drilled through the stud. After the drill bit is removed, an "easy-out"-type bolt extractor is used for removal. Such bolt extractors are formed with gripping teeth and/or shaped flutes adapted to engage the sides of a drilled bore in the broken bolt stud. The gripping surfaces remove the threaded bolt when the extractor is rotated in the direction opposite to that of the bolt threads.
Shortcomings of such tools are many. The drill bit is often broken in the process of drilling. This results in the two-fold problem of removal of both the broken bolt stud and removing the broken drill bit. Even when the drill bit is not broken, the bolt stud is often driven deeper into the threaded hole during the drilling process, making extraction more difficult. Many extractors require that the drilled hole be threaded, requiring an additional step of using a tap wrench to form the threads. Hence, always many separate tools and many steps are required. The many steps are tedious, time consuming and frustrating, and results are often unsatisfactory.
Herethroughout for clarity and simplicity, the bolt or stud will be considered as having right-hand threads--as by far the dominant number of bolts and studs do--and hands of threads and directions of rotation will be used as is appropriate for broken bolts with right-hand threads. This is in no way limiting: if the stud has left-hand threads, the hands of thread and directions of rotation will be opposite those taught herein.
The two above-mentioned patents describe inventions which combine a drill for forming a bore within a broken right-hand bolt stud and a bolt stud extractor for removing the broken bolt in a single combination tool, thereby enabling one to remove the broken bolt in one operation. The lower portion of the tool is provided with a drill bit having a cutting edge threaded with a pitch in a left hand direction (opposite to the threads of the broken right-hand bolt stud being extracted). In patent 4,777,850 the drill bit body is on the lower end of a threaded shaft the upper portion of which is structured to be connected to a suitable counterclockwise hand tool or power-driven tool.
A bolt extractor collet is threadedly mounted on the right-hand threaded shaft above the drill bit. The diameter of the lower portion of the gripping collet is less than the outside diameter of the drill bit which enables the collet to enter the bore formed in the broken bolt stud. The extractor collet is formed of a series of longitudinal segments separated by slots. The upper portion of the drill bit head is formed with an expander surface structured to engage and expand the longitudinal segments of the expander collet.
Preparatory to removing a broken bolt which remains within a threaded bore, the upper end of the shaft of the extractor is connected to a suitable hand or power drive tool.
To remove the broken bolt stud which remains in the bore, the drill bit engages the stud and rotates to form a bore within the body of the broken bolt stud. As the tool penetrates within the broken bolt stud, the extractor collet, which is threadedly mounted on the drill shaft, engages the interior of the hole being bored in the stud. Continued rotation of the tool causes the extractor collet to be "screwed" down toward the drill bit at the lower end of the shaft. Further rotation of the collet relative to the shaft causes the shaft to rise and the ends of the segments on the extractor collet to engage the expander surface on the drill bit body. This causes the segments to spread, thereby securely gripping the interior bore in the broken bolt stud just formed by the drill bit.
At that point, continued rotation of the drive means in the opposite direction with respect to the broken bolt stud threads simply "unscrews" the stud out of its threaded bore. The upper end of the expander collet serves to provide an additional surface for gripping by a hand tool, if needed, and also provides a means for separating the expander collet from the broken bolt stud after the stud has been removed. This is done by rotating the collet and stud member in opposite directions.